All the organisms of this kingdom are prokaryotes. Monera are considered as the most primitive group of organisms. They include various types of bacteria and blue-green algae. Monerans are most abundant of all organisms, due to their versatility of their habitat.It is estimated that a single drop of water contains 50 billion bacteria.
The Kingdom Monera includes organisms that are single-celled known as bacteria. The microorganisms in Kingdom Monera are considered as the most ancient living forms on earth. The kingdom is divided into two groups Archaebacteria and Eubacteria.
These cells do not have nuclear membrane, the chromosome is a single and circular, they also lack membrane bound cellular organelles.
This kingdom includes bacteria, cyanobacteria, mycoplasma etc. They are unicellular organisms and do not have specific mode of nutrition. They can be either aerobic or anaerobic.These organisms have cell wall which is made up of peptidoglycans. The cell organelles are not membrane bound. Cell organelles like endoplasmic reticulum, mitochondria are absent. Reproduction is by spore formation and binary fission.
General characteristics of the kingdom Monera are as follows:
- They are primitive organisms.
- All organisms of the kingdom are prokaryotes.
- They are present in both living and non-living environment.
- They can survive in harsh and extreme climatic conditions like in hot springs, acidic soils etc.
- They are unicellular organisms.
- Membrane bound nucleus is absent.
- DNA is in double stranded form, suspended in the cytoplasm of the organism,referred as nucleoid.
- A rigid cell wall is present.
- Membrane bound cellular organelles like mitochondria are absent.
- Habitat – Monerans are found everywhere in hot springs, under ice, in deep ocean floor, in deserts and on or inside the body of plants and animals.
- Nutrition – autotrophs – can prepare their own food heterotrophs – depend on others for food, saprophytes – feed on dead and decaying matter, parasitic – live on other host cells for survival and cause, symbiotic – in mutual relation with other organisms, commensalism – it is where one organism is benefited and the other is not affected, mutualism – where both the organisms are benefited.
- Respiration – respiration in these organisms vary, they may be obligate aerobes – the organisms must have organisms for survival; obligate anaerobes – the organisms cannot survive in the presence of oxygen; facultative anaerobes – these organisms can survive with or without oxygen.
- Circulation – is through diffusion.
- Movement – is with the help of flagella.
- Reproduction is mostly asexual, sexual reproduction is also seen. Asexual reproduction is by binary fission, sexual reproduction is by conjugation, transformation and transduction.
Kingdom Monera has been classified into two groups – Archaebacteria and Eubacteria.
Archaebacteria are microbes that live in extreme and harsh conditions, they are known as extremophiles. These bacteria lack cell wall, their cell membrane is made up of different lipids, and their ribosomes are similar to that of eukaryotes.
Archaebacteria are of three major groups of bacteria based on their habitat i.e., thermophiles, halophiles and methanogens.
Eubacteria are true bacteria. The characteristic feature is the presence of rigid cell wall and if present a motile flagelllum that aids in locomotion.These organisms are characterized based on their nutrition and their shapes.